1. Field of the Invention
This invention relates to a process for the preparation of cellular polyurethanes, using liquid adducts of mono- or polyamines containing one or more hydroxyl groups and carbon dioxide, in particular with the addition of liquid carbonic acid salts of such hydroxyl group-containing mono- or polyamines.
2. Description of the Invention
The use of carbon dioxide addition products of hydroxyl group containing amines (hereinafter called: hydroxylic amines) for the preparation of polyurethanes is known per se and the use of ethanolamine carbamate in a process for the production of a cellular polyurethane elastomer is mentioned in DE-OS 2 200 480, but this prior publication does not disclose whether the ethanolamine carbamate is in the solid or liquid state. DE-PS 2 621 582, however, reveals that carbamates which are reaction products of primary or secondary amines containing one or two hydroxyl groups and carbon dioxide are solid and are obtained in the solid state if they are prepared by introducing carbon dioxide in an alcohol or other solvent, and cannot form a homogeneous, monophasic mixture with a polyol. The last mentioned prior publication does not disclose that the carbon dioxide addition products in question are liquid at room temperature or that they can be obtained as liquids.
It is known from DE-OS 1 570 571 that liquid carbamates of compounds containing amino groups do exist. The amines mentioned in the said prior publication are, however, limited to diamines or polyamines containing ether groups, wherein from 0.1 to 50% of the amino groups may be replaced by hydroxyl groups. In this reference it is preferred, however, to use high molecular weight or relatively high molecular weight amines generally having only a low basic nitrogen content and with the amino groups frequently attached to secondary carbon atoms, so that the amount of carbon dioxide taken up is low.
The use of products according to DE-OS 2 200 480 and DE-PS 2 621 582 for the production of polyurethane foams is also known.
The state of the art therefore does not provide the man of the art with the possibility of using liquid, low viscosity carbon dioxide adducts of hydroxyl group-containing mono- or polyamines with a high amine and carbon dioxide content for the production of polyurethane foams, and in particular, no homogeneous, optically clear, monophasic, stable mixtures of such carbon dioxide adducts and polyols containing at least two isocyanate reactive hydrogen atoms are known.
It has now surprisingly been found that carbon dioxide adducts of mono- or polyamines containing one or more hydroxyl groups, in which the amino groups may be primary and/or secondary and possibly also tertiary and may be substituents on or chain members in acyclic or cyclic aliphatic compounds are obtained in a liquid form and remain liquid without crystallization if they are prepared by addition of the hydroxyl-containing amines to carbon dioxide and optionally water, and that the adducts prepared by this method are homogeneously soluble in the polyols conventionally used for the preparation of polyurethanes, in particular polyols having a functionality of .gtoreq.2 and a molecular weight of from about 60 to 200.
In particular, it has also surprisingly been found that not only carbamates, which are ammonium salts of alkyl carbamic acids, but also salts of carbonic acid with these polyamines containing hydroxyl groups, which salts are obtained by carrying out the reaction of the amines with carbon dioxide in the presence of water, and the mixtures of salts of the carbamic acids and carbonic acid, are liquid. The differences between carbamates as salts of carbamic acid and carbonates or bicarbonates as salts of carbonic acid are well known to the man of the art and have been described, for example, in A. Smola, Mitteilungen des Chemischen Forschungsinstituts der Wirtschaft Osterreichs 2, 38-40 and 43-45 (1948) (Chemical Abstracts 43 (1949), 6157 h).
The fact that liquid carbonic acid salts of amines containing hydroxyl groups are now available also makes it possible to overcome the disadvantages of the carbamates of such hydroxyl group-containing amino compounds known in the art. Thus it is mentioned in DE-PS 2 621 582 that amino carbamates of the aforesaid "amines are generally hygroscopic" and that "the aminocarbamate which has been synthesized separately, isolated and purified is difficult to store in the form of a fine powder" and that there is "insufficient dispersion in the polyol".
DE-OS 2 200 480 teaches that the aminocarbamates are generally no longer heat stable at temperatures from about 35.degree. C. and decompose at such temperatures. A similar teaching is given in DE-OS 1 570 571, according to which conversion of the amines into carbamates by reaction with CO.sub.2 can only be carried out at temperatures of from -40.degree. C. to 40.degree. C., preferably from 0.degree. C. to 20.degree. C. The carbamates prepared by way of example in this prior publication for the most part already decompose at room temperature or at 30.degree. C.
The liquid carbon dioxide adducts according to the present invention, on the other hand, are surprisingly stable. They are prepared at temperatures of up to 80.degree.-90.degree. C. or even higher and vigorous uptake of carbon dioxide in some cases only begins at this temperature. The hygroscopic character mentioned in the prior publication as a disadvantage of the crystalline carbamates of the hydroxyl-containing amines is now of no importance since the (hydrogen) carbonates which are assumed to be formed from the carbamates by uptake of water are in any case liquid and suitable for the preparation of cellular polyurethanes. Moreover, the liquid carbamates according to this invention were not observed to have any pronounced tendency to absorb water. The carbamates and (hydrogen) carbonates according to the invention could also be subjected to prolonged heating to temperatures up to 100.degree. C., e.g. 50.degree. C., and could be subjected to a vacuum at room temperature, e.g. of 20 mbar, without any evolution of carbon dioxide or loss of water being observed.
Liquid carbamates and (hydrogen) carbonates of hydroxyl group-containing amines, in particular (hydrogen) carbonates having such properties could not be inferred from the published state of the art, nor could their use in a process for the production of foamed polyurethane and/or polyurea resins, in which, by virtue of their stability, solubility and liquid aggregate state, they are more easily worked up than the carbamates and carbonates known in the art.